Discovering the bold function doesn't make something true. Of the shows that were canceled most weren't done so because of ratings but because the shows were so old they became too expensive. Angel was canned because it didn't "fit the direction of the network" which was apparently down the toilet.
Most shows in the west aren't designed with a defined end in mind. Most shows, nearly all shows, are designed to be non linear by nature. Low ratings or budget issues are therefore the reason for cancellation for nearly all shows. This doesn't mean that they show up the studio one day and find out they were fired. They find these things out, usually, weeks or months ahead of time. Most of these shows knew they were going out and yet they still chose to go out open ended with several key plot and character arcs unresolved.